The purpose of a crash barrier is at least two-fold. The primary purpose of the crash barrier is to protect structures that are located near a road or highway from damage resulting from impacting vehicles. Repair of roadside structures such as road dividers and bridge stanchions is not only expensive, but highly disruptive to traffic flow. Given the high public awareness of traffic injuries and fatalities, another purpose of the crash barrier is to help reduce injuries to persons riding in a vehicle that would otherwise collide directly with the roadside structure.
Rigid guard rails are well known in the art to deflect the impact of a vehicle away from road hazards and to protect roadside structures. The rigid guard rails are positioned alongside the road between the general direction of traffic flow and the roadside structure. But rigid guard rails fail to provide adequate protection to the roadside structures and vehicle passengers because the guard rails absorb only a small percentage of the impact energy of the oncoming vehicle. The rail guards may also fail under the impact of the collision.
U.S. Pat. Nos. 3,674,115 and 3,944,187 disclose impact attenuation devices having an array of buffer elements wherein sections of the arrayed buffer elements are separated by diaphragms and the entire array of buffer elements is surrounded by fenders. The fenders and diaphragms, combined with a base framework and a system of cables, springs, and restraining pins hold the buffer elements in the arrayed configuration. Upon the impact of an oncoming vehicle, the sections of the arrayed buffer elements sandwich together, the fenders and diaphragms crushing onto the buffer elements. The individual buffer elements have chambers or cells formed therein. The chambers of the buffer elements disclosed in U.S. Pat. No. 3,674,115 are filled with a liquid substance. Under the impact of an oncoming vehicle, the chambers are compressed and the pressure of the fluid within the chamber increases. The pressure within the chamber is released at a controlled rate through a series of orifices so that the energy of impact is dissipated. The chambers of the buffer elements disclosed in U.S. Pat. No. 3,944,187 are filled with a solid material such as vermiculite. Under the impact of an oncoming vehicle, the volume of the chambers is compressed, which tends to load and disintegrate the vermiculite, thereby dissipating the impact energy. The buffer elements are intended to absorb some of the energy of an impacting vehicle.
The impact attenuating devices of U.S. Pat. Nos. 3,674,115 and 3,944,187 may be to some extent reusable. The base framework, diaphragms, and fenders may be pulled apart, the cables, springs, and pins reattached or replaced. The liquid or solid material in the chambers of the buffer elements can be topped off or replaced, though many if not all of the buffer elements would probably need to be replaced. After the impact attenuation devices suffer the impact of a vehicle collision, they require extensive maintenance from a maintenance crew trained to repair the particular type of impact maintenance device. Depending on the ready availability of maintenance crews and replacement parts, the impact attenuation device may not be restored to serviceability for several days or weeks. Meanwhile the roadside structure is exposed to the threat of a second vehicle impact without adequate protection. Passengers in passing traffic are also exposed to an increased risk of serious injury if a vehicle collides with the damaged impact attenuation device or the device fails under a the impact of a second collision.
U.S. Pat. No. 4,452,431 discloses an improved fender panel for these impact attenuation devices. The improved fender panels are intended to help the damaged or unrestored impact attenuation devices better withstand a second vehicle impact. The fender panels are less likely to be severely deformed upon the impact of an oncoming vehicle, therefore, the fender panels are more likely to be reusable. But despite the improved fender panels, these impact attenuation devices are expensive to maintain and require substantial road crew service after every minor impact.